Field
The described technology generally relates to a display device.
Description of the Related Technology
A flat display device such as a liquid crystal display or an organic light-emitting diode (OLED) display includes a display panel including a matrix of pixels having switching elements and display signal lines. The display also includes a gate driver that supplies gate signals to gate lines so as to turn the switching elements on and off, a data driver for applying the data voltage to a data line, and a signal controller for controlling the above elements.
The gate driver and the data driver can be mounted on the display device as an IC chip type, a flexible printed circuit film as a tape carrier package (TCP) type and attached to the display device, or a printed circuit board (PCB).
An OLED display has favorable characteristics in terms of power consumption, response speed, viewing angle, and contrast ratio since it does not require an additional light source. Further, OLED technology allows reduction in thickness and superiority in luminance and color purity (wide color gamut), thereby having applications as a flexible display.
Each OLED includes a pixel electrode, an opposed electrode, and a light emission layer interposed therebetween. One of the pixel electrode and the opposed electrode serves as an anode, and the other serves as a cathode. Electrons injected from the cathode and holes injected from the anode are combined in the light emission layer to generate excitons, and the excitons release energy to emit light. The opposed electrode is formed across the pixels to receive a predetermined common voltage.
The pixels included in such a display device are positioned in a display area where an image is displayed, and a switching element included in a pixel constituting a pixel driving circuit can include at least one thin film transistor (TFT). For example, a pixel driving circuit of an OLED display includes at least one TFT connected to an OLED.
Characteristics of TFTs included in the pixels positioned in the display area can experience variances due to manufacturing process factors. For example, although no abnormal operation may occur during while at room temperature, problems can result from extreme conditions such as a relatively high or low temperature. When there is a problem with the TFTs, it can affect the quality of the displayed image. Accordingly, it is necessary to inspect the TFT characteristics (e.g., a threshold voltage) included in the pixels of the display device.
However, when directly measuring the characteristics of the TFTs positioned in the display area, the thin film transistor can be damaged. For that reason, a test unit is formed at a portion (e.g., a peripheral portion) of a display panel. The test unit can include a TFT having a characteristic that is similar to those of the TFTs positioned in the display area. This test unit is also referred to as a test element group (TEG) pattern. It is possible to measure the current of the TFT of the test unit by applying a voltage through a pad unit connected to the test unit in order to determine the quality of the TFT of the pixel formed in the same process as the process during which the TFT of the test unit is formed.
However, a peripheral pattern condition of the TFT of the pixel positioned in the display area is different from that of the test unit, and as a result, a value measured in the test unit may not reflect an actual characteristic of the TFT of the display area. Accordingly, there is a large difference between the characteristics of the test unit and the display area.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it can contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.